Those skilled in the art will appreciate the wide utilization of frequency synthesizers in modern day transceivers. An example of a conventional frequency synthesizer is illustrated in FIG. 1. The synthesizer 100 is comprised of a reference element 102, which may be any suitable crystal oscillator circuit or temperature compensated oscillator module. Ideally, since the frequency stability of the entire synthesizer 100 is determined by the stability of the reference frequency, the reference element 102 should provide an extremely frequency stable reference signal. A reference divider 104 receives the waveform provided by the reference element 102 and divides the signal by an appropriate amount to present a useable frequency to the phase detector 106.
Generally, a divided frequency range from 5 kHz to 30 kHz is suitable for most land mobile applications. The phase detector 106 compares the phase of the divided reference signal 105 (provided by the divider 104) and a signal provided by a loop divider 108. The phase detector 106 provides an output signal 110, which is dependent upon the phase difference between the signals supplied by the reference divider 104 and the loop divider 108. The phase comparison signal 110 is filtered by a loop filter 112 to filter noise and spurious energy to prevent unwanted modulation of the voltage controlled oscillator (VCO) 116. The filtered signal 114 is coupled to and controls the VCO 116 as is generally known in the art. The loop divider 108 "closes the loop" by dividing the output of the VCO 116 to provide a signal having a like frequency as the reference divider 104. In this way, the frequency of the VCO 116 is "locked" to the reference element as is known in the art.
Typically, each of the functional blocks of FIG. 1 are implemented using discrete elements, and small scale integration (SSI) devices. Each circuit of the frequency synthesizer consumes precious printed circuit (PC) board area, which defines the overall size of the frequency synthesizer. Those skilled in the art will appreciate that the current trend of modern-day transceivers is towards circuit miniaturization and improved circuit performance. However, improving the rudimentary frequency synthesizer of FIG. 1 generally tends to increase PC board area, thereby presenting a transceiver designer with conflicting performance/size design choices. For example, to provide a multi-frequency synthesizer it is known to make the reference divider 104 and the loop divider 108 programmable. Also, elaborate loop filters and phase detectors have been used to improve synthesizer "lock time". Each of these improvements require the use of more components leading to a larger frequency synthesizer. As is known in the art, additional parts consume more power, generate more heat, consume more PC board area and tend to reduce reliability.
Therefore, there is a need in the art for a high performance frequency synthesizer that consumes little PC board area while providing improved operational characteristics over the frequency synthesizers of the prior art.